The present invention relates to a card cage for printed circuit boards and more particularly to an improvement in a dual density printed circuit board (PCB) card cage.
Printed circuit board card cages conventionally include a pair of spaced apart frame members having a plurality of parallel grooves or channels on their inner surfaces to define guide and support slots for printed circuit board cards. Printed circuit board cards are then retained by these guide slots in parallel spaced relationship between the frame members. A dual density PCB card cage comprises a pair of back-to-back card cages for supporting two sets of printed circuit board cards in a stacked relationship. Conventionally, dual PCB card cages include top and bottom frame members and a pair of back-to-back intermediate frame members for cooperation, respectively, with the top and bottom frame members. Each of the frame members is provided with a plurality of guide and support grooves for supporting and guiding PCB cards into a functioning position.
The prior art shows several efforts relating to the construction of dual PCB card cages. The Etchison, Jr., et al. U.S. Pat. No. 4,353,469 relates to a support shalf for PCB cards and discloses a dual density structure. Although this patent discloses an intermediate support frame which includes means on both its upper and lower surfaces for supporting and guiding the edges of PCB cards, the upper and lower surfaces of this intermediate frame member are vertically spaced from each other and include their own set of guide members. The Leger U.S. Pat. No. 4,327,835 and the Erb U.S. Pat. No. 3,377,515 also relate to dual density PCB card cage constructions. Both of these also comprise a single intermediate frame member; however, they both have individual and separate guide and support inserts which are adapted to be snapped into the intermediate frame member. The Reynolds et al. U.S. Pat. No. 3,733,523 relates to a dual density PCB card cage and includes a single intermediate frame member having a plurality of grooves or channels on opposite sides for purposes of supporting and guiding PCB cards. This intermediate frame member, however, is comprised of a thick-walled panel which appears to be constructed of molded plastic or some other similar material.
Although several attempts have been made in the prior art to provide a dual density PCB card cage which is of relatively inexpensive, simple in construction, yet strong and rigid enough to provide the close tolerances required in a device of this sort, none has been completely successful. Accordingly, there is a need in the art for a dual density PCB card cage having a construction which is relatively simple and inexpensive and which is also strong enough to maintain the structural rigidity needed.